The invention relates to techniques for modulating carrier signals, and more particularly to techniques for modulating a carrier signal independently of the amplitude, frequency, and phase of the carrier signal to cause each half cycle of the carrier signal to represent the state of a plurality of digital bits, and to techniques for demodulating such a carrier signal, and to techniques for generating frame markers therefore.
A variety of modulation techniques are very well known, including amplitude modulation, frequency modulation, and phase modulation. Although it is possible to transmit digital pulses directly along a communications medium, especially a wire or optical medium, it usually is not practical to transmit large amounts of data directly in digital form via a wireless communication link. Consequently, digital data is "encoded" into high frequency modulated carrier signals using various pulse coded modulation (PCM) techniques, such as high frequency shift keying (FSK) techniques. All of these techniques require at least several cycles of the carrier signal for each digital bit transmitted.
Such digital data, encoded in analog form into modulated high frequency sinusoidal carrier signals by well known modulation techniques, is often received by a receiver and stored as received on magnetic tape for archival purposes, and when it is necessary to be retrieved from the magnetic tape, the modulated signals are played back from tape, fed into a demodulator, and then converted to digital form.
The state of the art in transmission of digital data and modulation techniques is believed to be indicated by U.S. Pat. Nos. 3,993,862; Re-issue 30,182; 4,106,007; 4,227,250; 4,236,248; 4,339,823; 3,764,743; 3,821,481; and 3,755,739.
It would be desirable to have a technique for inexpensively modulating a carrier signal independently of its frequency, amplitude, and phase. It would also be desirable to have a technique for encoding or modulating a carrier signal to contain information which can be faithfully demodulated, despite considerable distortion imposed upon the modulated carrier signal by the communications channel. It would also be desirable to have a technique for encoding or modulating a carrier signal so that every half cycle of the carrier signal contains information representative of the logical states of a plurality of digital bits. It would also be desirable to have a more economical, higher density storage of digital information than is presently available.
Therefore, it is an object of the invention to provide a new and improved system and apparatus for modulating a carrier signal independently of its frequency, amplitude, and phase.
It is another object of the invention to provide a system and method for modulating a carrier signal so that each half cycle of the modulated carrier signal contains information which represents the states of a plurality of digital bits.
It is another object of the invention to provide a system and method for modulating and demodulating a carrier signal so that the demodulated information faithfully reproduces the modulation data despite severe distortions imposed upon the modulated carrier signal by the communications and/or recording medium.
It is another object of the invention to provide a technique for greatly increasing the amount of digital information that can be stored in an encoded analog format on magnetic tape or other media, such as plate optical media or other media capable of recording analog signals.
It is another object of the invention to provide a modulation and demodulation signal that greatly increases the amount of information that can be communicated on a communications channel.
It is another object of the invention to provide a system and method for greatly increasing the speed at which analog and/or digital information can be communicated through a communications channel.
It is another object of the invention to provide a new modulation/demodulation technique that can be used to independently modulate/demodulate signals which are simultaneously being modulated or demodulated using prior modulation/demodulation techniques.
It is another object of the invention to provide a highly efficient digital encoding format that is compatible with conventional video systems so that relatively inexpensive conventional analog hardware can be utilized by digital data systems.
It is another object of the invention to provide an inexpensive and effective means of digital audio recording and playback.
It is another object of the invention to provide a modulation technique that can make the recording, transmission and playback of digital image video much less expensive than it has been heretofore.